In the field of computational mechanics, surrogate models, which replace part or all of numerical calculations with machine learning such as deep learning, are attracting attention. A wide variety of numerical calculations have been studied for surrogate models, but it is difficult to model phenomena involving plastic deformation, especially buckling, and there are still few examples. In this study, a surrogate model was constructed for the simulation of the bending test of hat-shaped steel with such a bucking. We have constructed a model that can predict the bending position, amount of deformation, and stress distribution.

The structural strength evaluation of crash boxes is predicted by machine learning in this study. The training data was obtained from the dynamic elastic plastic analysis of the crash box. The input physical quantities are barrier angle, box thickness, material properties and mass equivalent to vehicle weight. The output physical quantity is the reaction force. Buckling occurs in the analysis and different directions of corruptions are one of the most interesting phenomenon from a point of engineering view. Physically meaningful features that take into account physical laws, physical properties, shape, and so on were added. As a result, we showed that learning by CNN is possible with higher accuracy. In addition, data design and data augmentation that takes physical phenomena into account are necessary to deal with large outlier. We would like to propose an adaptive method for machine learning in structural evaluation that can be used for a wide range of structural evaluations.

In order to shorten the design process of industrial products, an alternative evaluation methodology to CAE is needed. Machine learning methodology is one such method. The authors have applied convolutional neural networks (CNN) to regression problems. Although CNNs are highly capable of interpolating nonlinear physical phenomena, the design of input data should be carefully considered when training on less sensitive data with a small training data set. In this paper, CNNs are adapted to predict crash simulations of a finite element method model that mimics the pedestrian leg protection performance test prescribed by JNCAP.

A convolutional neural network, which reproduce a function by data, was used to predict the amount of warp distortion of a four-layer circuit board in a reflow soldering process. The data used for training are material properties such as Young's modulus, board thickness, and residual copper content as input data, while the warpage strain data to be predicted is the amount of warp of the circuit board obtained from the measurement. Since several distortion data to be predicted was insufficient to be used for training, a newly proposed data augmentation method used to increase a total amount of data. Proposed data augmentation is evaluated through the result of the predictions and discussed.

For the purpose of accelerating numerical analysis, we propose a surrogate model for a particle method based on IsoGCNs, which are variants of graph neural networks (GNNs). In mechanical phenomena, when transformations such as rotations, translations, and reflections are applied to the input, the output takes on the same transformations. This property is called equivariance. IsoGCNs improve learning efficiency by introducing the equivariance into GNNs, and have been shown to be useful for finite element methods. This study shows an IsoGCN formulation for the particle method by considering relationships between particles as a graph. The proposed method is verified by comparing the errors and computation time of numerical and surrogate analyses of the three-dimensional heat conduction equation. In this paper, the problem of estimating the temperature distribution after one second from the initial temperature distribution is considered. As a result, the surrogate analysis requires more computation time than the numerical analysis with a time step size of one second. However, the accuracy is comparable, and it confirms that it can learn three-dimensional heat conduction equations.

In many cases, results of flow analysis are visualized by contour lines or contour color surfaces with prescribed values (or functions), or by markers indicating flow features such as vortices or shock waves. However, in the case of newly analyzed flow fields, or of complicated flow fields, we must not know what to visualize in advance. The present authors have been researching of the method automatically visualizing results of flow analysis, by classifying the flow and giving color to the flow by SOM (Self-Organizing Map). In this paper, the usefulness of the present approach to compressible flow analysis is discussed.

As an evaluation method for concrete structures, it is believed that information from hammering inspections can be digitized by AE sensor and predicted by machine learning. In this study, XGBoost, which can visualize the importance of input factors, was used to predict the internal condition of concrete structures. The results of hammering inspections of concrete specimens were used for learning, and predictions were made for four types of concrete structures: reinforced concrete, spiral sheathing, expanded polystyrene and unreinforced concrete. Through the forecasting results on this data set, an evaluation was conducted sampling techniques were discussed.

Digital hammering inspection using acoustic emission (AE) sensor is expected to be a method to investigate for improper construction of stud dowel in concrete structures. AE sensor measure vibration waveforms using mechanical resonance of piezoelectric elements. Since there is no established method for the predicting the state of the stud dowel using the waveforms obtained from AE sensor, machine learning, such as random forests and XGBoost, is used to make predictions. The features used for prediction are the decay time and the frequency and amplitude of the waveform when it was converted to the frequency domain by the fast Fourier transform. Binary classification is used to predict whether an abnormality of stud dowel is present or not. It is possible to improve the accuracy by dividing the data according to the state of the stud dowel.

This study is present a numerical method to suppress the mesh dependency in strong discontinuity analysis by the finite cover method (FCM) that is known as a generalized finite element method. To realize fracture process from nucleation to propagation of discontinuity, a seamless crack propagation analysis is combined with the moving least squares method (MLSM), by which standard shape functions are enriched for nodes outside the associated physical cover. Thus, the displacement field is determined by not only the nodes associated but also the non-associated ones. When the integral domain of a finite cover is separated by the discontinuity surface, it sometimes becomes too small to calculate a proper solution. Thus, the displacement field is determined by not the nodes associated with the finite cover but ones around it. In other words, the nodal degrees of freedoms corresponding to the small integral domain of the cover is cut off from the global stiffness matrix. The capabilities of the developed numerical method are demonstrated throughout simple numerical examples.

The contribution of this study is to propose a cohesive traction embedded constitutive law to predict the changes of ductile failure under different mixed mode. Flat and shear-lip fractures in ductile failure under different mixed mode are represented by the cohesive traction-separation law and shear-induced damage, respectively, reflecting that these mechanisms are different from each other. For the flat fracture, the stiffness reduction and strain softening due to void nucleation, growth, and coalescence under high stress state are realized by the cohesive traction-separation law that determines the process of stress releases along with ductile crack opening. To realize crack nucleation at an arbitrary location and propagation in an arbitrary direction, the cohesive separation law is combined with the Hencky-type hyperelastic-plastic model by the introduction of apparent deformation gradient due to crack opening and local balance equations between cohesive tractions and principal stresses. On the other hand, for the shear-lip fracture, the shrink of yield surface caused from the evolutions of micro voids in a shear band is represented by the shear-induced damage variable that is incorporated into the Tresca yield function. Moreover, the evolution of shear-induced damage is determined by the damage loading function corresponding to the plastic energy release based on thermodynamics. Simple numerical examples are presented to demonstrate that our proposed model enables us to predict the change of ductile fracture under different mixed mode.

It has been confirmed by experiments and crystal plasticity analysis that a vertex is formed at the loading point of the yield surface in the stress space during plastic deformation. However, most past deformation analyses for crack tip behavior have used plasticity models with a classical normality flow rule. In this study, we introduce a non-normality flow rule, which considers the formation of a vertex on the yield surface. We investigate the effect of vertex formation on Mode I crack growth behavior for cyclic loading. Numerical results show that both crack tip opening displacement and crack growth are greater for the model with the non-normality flow rule than for the standard normality flow rule. The distribution of equivalent plastic strain near the crack tip indicates that the model with the non-normality rule leads to localized plastic deformation, which is not seen in the case where the standard normality flow rule is adopted.

The nacre-like biomaterials, which are being studied more and more by scientists, exhibit a perfect combination of toughness and strength thanks to their hierarchical microstructure made up of alternately soft proteins and hard mineral tablets. Recent investigations have revealed a correlation between fracture toughness and fracture patterns such like crack bifurcation and crack deflection. However, the relationship between the fracture patterns and toughness of the nacre-like biomaterials hence requires more investigation. In this study, we investigated the Mode I crack extension and microstructure deformation near the crack tip, in small scale yielding condition, using incremental finite element method. We identified the microstructure-dependent brittle-ductile transition and the 3 associated fracture patterns. We discovered the mechanism of how microstructure affects fracture patterns and brittle-ductile transition, and hence fracture toughness. These findings will help to explain the toughening mechanism associated with crack extension, which will provide a clue to the design of nacre-like artificial materials for high applicability.

This study has investigated the effects of coil turn position on the principal stresses and the correction factors, F_i (i=I, II and III) of the three modes of the stress intensity factors for a semi-elliptic surface crack on the outer surface of a compression coil spring. For this purpose, 3D finite element stress analyses have been made on a compression coil spring having a surface crack on the outer surface of its wire at every 0.5 turn from n=0.5 to n=4.5. The maximum principal stress, σ₁, was also calculated by FEM and found to vary as cosine function of number of turns, n. The value of σ₁ took maxima for half integer coil turns, i.e., n=0.5, 1.5, 2.5, …, whereas minima for every coil turn, i.e., n=1, 2, 3, … The principal stress fluctuation range was found as small as 4.6 % of its center value. The correction factor F_I for the mode I stress intensity factors of the semi-elliptic surface crack also varied as cosine functions of n in the same manner as σ₁ at all the positions of crack peripheries investigated. The largest mode I correction factor fluctuation range was as large as 22.9 % of its fluctuation center value. The variations of F_I value with n can be distinguished into 5 groups according to the distance from the wire surface. This tendency was caused by the variations of F_I value with the eccentric angle φ of the crack which are expressed as quartic functions of φ almost symmetric with the φ=90° (deepest point). The F_I value took minima at the wire surface and second minima at the deepest point of the crack, and the value increased as the point got closer to the surface. The F_I value varied from 0.47 to 0.69 with the geometrical parameters n and φ. The F_I value was found dominant among the three modes of correction factors, since the values of the correction factors of the other modes, i.e., F_II and F_III, were at most 8.3 % and 14.3 % of the F_I value, respectively.

The validity of the crack propagation criterion under extremely low cycle fatigue due to earthquakes is still under discussed. Existing evaluation parameters are difficult to apply because they change under the constraint of restraining effects due to large plastic deformation. In a previous study, the crack propagation criterion was proposed and evaluated using equivalent plastic strain amplitude and stress triaxiality at the center of the plate thickness. Those parameters are physical quantities that are difficult to obtain from fracture experiments. In this study, the equivalent plastic strain amplitude and stress triaxiality at the crack front were analyzed under three different loading conditions to evaluate the applicable range in the direction of the plate thickness other than the center of the plate thickness and to improve the equation to be applicable near the plate thickness surface. As a result of the evaluation of the range of applicability in the thickness direction, it was found that the crack does not propagate near the surface in some cases.

The prediction of fracture behavior under extremely low cycle fatigue due to excessive loading is necessary for the life assessment of structures. ΔJ criterion has been used to assess the life under low cycle fatigue. However, the applicability of this method is not well confirmed under extremely low cycle fatigue. The reason is that fracture toughness is dependent on the loading conditions and geometry due to the constraint effect. In the previous study, the crack propagation criterion was proposed for a 1T-CT specimen of SUS316, focusing on the stress triaxiality and the equivalent plastic strain increment. However, no comparison has been performed for specimens of different shapes or materials, and more detailed verification is required. In this study, we performed generation phase and application phase analyses on 1.5T-CT and MT specimens. The results of both the generation and application phase simulation are in good agreement with the experimental results.

The strength evaluation of structures that requires high reliability, such as power generation facilities, is extremely important. It is necessary to ensure safety under extremely low cycle fatigue caused by earthquakes. However, a highly reliable evaluation method has not yet been developed because of variable fracture toughness due to the constraint effect with large deformation. The crack propagation criterion proposed in the previous study was confirmed validity under restrict condition. However, it is not considered constraint effect such as thickness and material properties. The objective of this study is confirmed whether the crack propagation criterion proposed in the previous study can apply changing of constraint effect. Furthermore, we propose the crack propagation criterion considered constraint effect under extremely low cycle fatigue.

Early Light Water Reactor Plants (LWR plants) in Japan are nearly 30 years old and utilities have been conducting technical evaluations of facility aging. Accurate prediction of fracture behavior for ductile materials is one of the most important issues to guarantee the integrity of the structure such as pipes in plants. If a crack is detected during the in-service inspections, the structural rational maintenance of the cracked pipe has been promoted based on the defect evaluation methods specified ASME Boiler and Pressure Vessel Code and JSME Rules on Fitness-for-Service for Nuclear Power Plants. Recently, experiments and simulations have been performed on pipes subjected to bending and torsion loadings. However, the failure criterion is still under investigation, and it is significant to propose a method to evaluate it appropriately. In this study, a finite element model of a large circumferentially cracked stainless steel pipe was generated and elastic-plastic analysis of stationary crack and crack extension were performed to validity of the results.

Crack propagation velocities depend on various mechanical factors and others. Propagating crack acceleration is not special phenomenon in material fracture problems, it can be caused under simple quasi-static tensile loading. However, the general theory to determine crack propagating velocity is not established. In this study, generation phase simulation is demonstrated to discuss mechanism for crack accelerations. Crack propagation history, crack propagation start timing and constrained displacement conditions in the numerical analysis are based on the experimental fracture tests. Crack propagation behavior is treated by the moving finite element method. J integral are evaluated in the numerical simulation.

Loading histories in numerical simulation is agreed with experimental result. Interrelation between time derivative of dynamic J integral and propagating crack acceleration are shown from the numerical results.

In this study, a three-dimensional finite element method analysis is carried out to analyze the crack propagation in a carbon steel (STS410) pipe with a circumferential through-crack in the lower center under a monotonic load by four-point bending. Validity of present analysis is then verified by comparing with experimental results under the same conditions. In addition, a crack growth analysis is performed on a flat plate with a through crack in the longitudinal direction under a monotonic tensile load, and J-values for cracks in the pipe and flat plate are obtained and compared.

In welded joints, which are widely used in various applications, the mechanical properties of material change discontinuously due to the effects of temperature history and weld between dissimilar materials. Therefore, it is necessary to develop a method for evaluating fracture mechanics parameter for structure with discontinuous changes in mechanical properties. One of the fracture mechanics parameters to evaluate crack propagation is the J-integral. The objective of this study is to establish an accurate mechanical strength evaluation method for problems with discontinuous changes in mechanical properties. For this purpose, we propose a three-dimensional J-integral which is applicable to large-deformation elastic-plastic problems that allow continuous and discontinuous changes of mechanical properties.

The purpose of this study is to make it possible to perform a large number of paratric analyzes on the position and shape of cracks under finite elasto-plastic deformation. In this report, we propose a one-way coupled analysis method using displacement interpolation between a global finite element method analysis model created without assuming cracks and a local finite element method analysis model assuming cracks. The proposed method is based on the superconvergent patch recovery, and uses the least-squares method to apply the nodal displacements of the global finite element model to the nodes of the local finite element model as displacement boundary conditions. In addition, we will create an merged finite element method analysis model assuming a crack directly in the global finite element method analysis model and identify the application conditions that can be applied to the problem without loss of accuracy through relative comparison by J-integral calculation at the crack tip which is nonlinear fracture mechanics parameter.

In recent years, there has been a need to develop safety evaluation methods for structures such as power generation facilities in overloading. However, the failure criterion for cracks in structures under extremely low cycle fatigue is not clear. In addition, the fracture criteria proposed in previous studies have not been sufficiently verified in terms of the applicable range. Therefore, the experimental results of fatigue crack propagation in SGV410 material with 1.5 inch CT specimens at stress ratios of R=-1.0 and -1.5 are reproduced by analysis using ΔJ as the crack propagation condition. The objective is to extend the applicability of the equation by correcting the failure criterion, which consists of stress triaxiality and equivalent strain increment, by the stress ratio. In this paper, the applicability of the fracture criterion to R=-1.5 is verified.

Safety evaluation of structures that requires extremely high reliability, such as power generation facilities, is essential. It is necessary to clarification of fracture criteria under extremely low cycle fatigue due to earthquakes, etc. It has been observed that the crack propagation rate changes at different stress ratios under high cycle fatigue, and a similar trend is expected to be observed under extremely low cycle fatigue. In this study, the purpose of paper is to propose the fracture criterion for crack propagation under extremely low cycle fatigue considering the effect of stress ratio for CT specimens with a thickness of 2 inches. As a fundamental study, crack propagation rate for different stress ratios was evaluated. In addition, the relationship between the crack propagation rate, which is closely related to the stress ratio, and the fracture criterion for crack propagation proposed in the previous study will be investigated.

In this study, a system for fatigue crack propagation analysis based on XFEM referred to as sim2d, which can model crack independently of finite elements, has been developed. A fatigue crack propagation analysis of a carbon steel CT specimen with stainless steel cladding has been performed by the system. The stress intensity factor for initial crack front obtained by sim2d is compared with that by FEM. In addition, crack propagation analysis was performed and the geometry of propagating crack front was simulated.

CFRP laminated composite structures manufactured by Automated Fiber Placement (AFP) may have gap and overlap defects and these potentially affect the strength of the structures. This study aims the development of finite element analysis models, which can consider strength reduction due to such defects. This paper proposes the modeling method considering ply-thickness variation induced by gap defects and shows the numerical results obtained by damage propagation analyses for the Open Hole Tensile Test of CFRP laminate with a gap defect.

A quasi-three-dimensional extend finite element method (XFEM) is applied to damage propagation analyses of carbon fiber reinforced plastics (CFRPs) laminate. An eight-node quadrilateral interface element and an eight-node hexahedral continuum element enriched with only the Heaviside function are used to model delamination and matrix cracks, respectively. Zig-zag enhanced cohesive zone model is introduced to a delamination and a matrix crack. The implicit static method is then used to solve system equations considering material nonlinearity. The results of damage propagation analyses were compared with experimental results obtained by the quasi-static indentation tests, and compression-after-impact tests. It was shown that the quasi-three-dimensional XFEM is an effective method for damage propagation analysis of CFRP laminates.

In semiconductors packages, heat generation density is increasing due to miniaturization. Since heat generation is caused by voltage input at the packages, electronic components are usually cooled by air. In recent years, electrification is widely spread among many engineering products like motor vehicles, and the amount of semiconductors packages installed in those products as well. To make the electronic components more densely installed, co-simulation of heat transfer analysis and electrical circuits is needed at designing products. In this paper, by using the Krylov-subspace model order reduction method, the accuracy of one-dimensional heat transfer analysis model concerning cooling effect of air is evaluated. By using the method, co-simulated with electrical circuits is possible.

Many bolted joints are used in the field of rolling stock. From the viewpoint of computational load, it is not realistic to employ a 3D detailed model including the contact of thread surfaces and bearing surfaces. In this study, the simplified shell-beam linear finite element model using interpolated rigid body elements, which was originally proposed for flat plate joints, is applied to outfitting attachment rail fasteners. The calculated strain distribution close to the fastener, stiffness against shear force, and natural frequencies are compared with those of experiments and detailed models. Since the detailed model well reproduces the experimental results, the accuracy of the simplified model is verified through the comparison with the detailed model. It is found that the coefficient of determination of strain distribution is larger than 0.73 and the differences in the stiffness against shear force and eigenvalues are less than 10 %. Therefore, the accuracy of our proposed model is well improved, as compared with the previous Naruse model.

We have proposed Analytical Iterative Uniaxial Stress Correction Method that corrects the average stress in this multiaxial state to the stress value in the uniaxial stress state by using iterative numerical simulations, and for some iron-based metals and aluminum alloys, the true stress - true strain curve in the entire strain range is obtained. In this paper, the validity of this stress correction method was verified using the design optimization / probability / statistical analysis tool LS-OPT.

Titanium alloys such as Ti-6Al-4V are widely used for aircraft engine parts due to their high specific strength. It is known that micro texture region, in which crystal orientations are locally concentrated in a specific direction, in titanium alloys causes a decrease in life due to cold dwell fatigue (CDF), where fatigue and room-temperature creep are superimposed. Therefore, we investigated the fracture mechanism and the life prediction method for CDF by calculating the stress and strain in and around the micro texture region by the crystal plasticity finite element method (CPFEM).

This paper provides a new vibration evaluation method of CT scanner with a non-axisymmetric rigid rotor. Vibration at the fundamental frequency under unbalanced load is expressed by the product of unbalance load and its transfer function obtained either by calculation of frequency responses function (FRF) or experimental measurement. Additionally, we provide a formulation of dynamic unbalance load for non-axisymmetric rigid rotor. Although applying correction weights is general way to eliminating residual vibration, but arbitrary weight set can be designed by satisfying the same unbalance load. Furthermore, optimization of the machine structure and the layout of units mounted in the rotor can also be made by evaluating transfer function of the machine with FEM and unbalance load, respectively.

The cloth simulation is applied to simulate the web handling process. Simulating the web handling process is challenging because of its thinness and the complex geometry when the wrinkle and folding occur, requiring stable calculation of the contact between the web and rollers. The cloth simulation has been widely used to generate realistic motion of cloth with wrinkles and folding for the computer graphics. The cloth simulation, however, is not based on the solid mechanics, and its applicability to the engineering field is still unclear. Therefore, the feasibility of the cloth simulation on the engineering purpose was demonstrated in this study. Applying the cloth simulation to the web handling process, the folding was simulated successfully when the mesh was small enough, the friction coefficient was high, and the degree of misalignment was large. Although the misalignment angle and the friction coefficient to generate the folding have not agreed quantitatively with the experimental data, the cloth simulation can be used to predict the web behavior potentially.

This study proposes an interpolation-based fast multipole method to reduce the computation time and memory consumption of the time-domain boundary element method (TDBEM) for 3D electromagnetic scattering problems. In this article, the formulation of the fast TDBEM is verified numerically in comparison with the conventional TDBEM as well as the reference solution with regard to computational accuracy, speed, and memory usage.

We design a topological phononic crystal in a thin plate, aiming at the development of an efficient elastic waveguide based on the concept of band topology in phonon dispersion. We adopt a snowflake-like structure for the crystal unit cell and search for the optimal structure that exhibits the topological phase transition of the three-dimensional phononic crystal by changing the unit cell structure. The bandgap width can be adjusted by varying the length of the branch of the snow side, and a topological phase transition occurs at the unit cell structure with three-fold rotational symmetry. Elastic waveguides based on edge modes appearing at interfaces between crystals with different band topologies are designed, and their transmission efficiency is evaluated numerically and experimentally. The results demonstrate robustness of the elastic wave propagation in thin plates. Moreover, we experimentally estimate a robustness of the topologically protected propagating states against structural inhomogeneities. The results obtained in this study pave the way for practical development of new surface acoustic wave technologies for high-frequency communication devices.

This lens can focus an incident plane wave to the diffraction limit in the direction perpendicular to the incident direction, but the peak width in the propagation direction is more than five times that. This phenomenon is a characteristic of Fresnel lenses, and this lens, which is a kind of lens, is also not avoided. It can be improved by increasing the width of the lens, whereas it is not practical. In this work, as an alternative method, we propose to arrange a point-like scatterer so as to partially cover the head. It is shown that the proposed method can suppress the spread of the focal spot at the focal point in the propagation direction.

We propose a topology optimisation of wideband periodic acoustic structures using the Padé approximation. The frequency of incident waves largely influences the performance of acoustic devices. We thus need to care about the performance deviation due to possible changes in the frequency when designing a practical acoustic structure. To this end, we may define the objective function for the topology optimisation as the frequency average of the performance index to take the frequency fluctuation into account. In the previous research, we proposed a topology optimisation with such an objective function, where the Padé approximation is used to efficiently estimate the frequency average of the sound pressure. The current research aims to apply the method to the optimisation of periodic structures. In this research, we use the energy transmittance across a structure as the performance index and define the frequency average of it as the objective function. The frequency average of the transmittance is derived via the Padé approximated far-field patterns in a certain frequency band. The topological derivative of the estimated objective function is also derived with the adjoint variable method. We confirm the correctness of the proposed method through a numerical test.

In this paper, we proposed a simulation method based on finite element method utilizing cyclic symmetry model to evaluate the deformation of inner grooved heat transfer tubes during tube expansion. The validity of the simulation method was confirmed by comparing the simulation results and experimental results for the deformation of inner grooved aluminum heat transfer tube due to tube expansion. Using the simulation method, we carried out a case study based on the orthogonal table for design of experiments and clarified the effects of design parameters such as groove depth, groove tip width, number of grooves, and lead angle on the deformation of inner grooved aluminum heat transfer tubes due to tube expansion. This made it possible to optimize the design of the heat transfer tube considering the depth change and tilt angle of the inner grooves caused by tube expansion.

Polymer composites with high thermal conductivity offer new possibilities for thermal management in electric systems. The objective this paper is to develop the prediction method of the thermal conductivity of polymer composites with high packing ratios of fillers. Fillers were spherical alumina and boron nitride with platelet shape. Measurements of thermal conductivity of polymer composites using steady state method and finite element analysis for thermal conductivity using representative volume element (RVE) models of polymer composites were carried out. The analytical thermal conductivity of multi-scale RVE models increased with increasing homogenization numbers and volume fraction alumina. When contacts between fillers were considered in RVE models, the finite element analysis results and experimental results were in good agreement.

Recently, COVID-19 has spread throughout the world, causing confusion among society and people. It is important to establish a framework for countermeasures against infectious diseases so that the outbreak will be under control in the near future and people can once again enjoy their lives and travel with peace of mind. In this study, it is proposed to evaluate whether the air in hotel rooms is correctly cleaned when air purifiers are installed, and to establish a framework for quantitative evaluation of safety against COVID-19 infection based on numerical fluid an analysis using OpenFOAM. The numerical models are measured at the Miyazaki Kanko Hotel. The flow field is assumed to be a three-dimensional, unsteady, incompressible viscous flow. Boundary conditions are given as velocities at the inlet and outlet surfaces based on the measured data. Nonslip conditions are set for the walls. This analysis uses RANS for turbulence analysis of the three dimensional incompressible viscous flow. The present analysis provides a visualization of the flow in a room, which is the basis for evaluating safety.

Recent advances in numerical computation technology have popularized wave acoustic analysis, which is used in the design of musical instruments. The goal of this study is to shorten the production time and reduce the cost of musical instruments by predicting the sound behavior of a violin as the object of analysis. The analysis model was created based on CT scan data of a Stradivarius violin, and the open software ADVENTURE_Sound was used as the analysis tool. ADVENTURE_Sound is characterized by its ability to perform detailed analysis with tens to hundreds of millions of degrees-of-freedom meshes and its high parallel efficiency even in massively parallel computing environments consisting of tens of thousands of processors. In conclusion, we confirmed that a steady-state analysis of a high-definition violin model is successfully performed with more than tens of millions of elements.

To numerically solve linear equations with large sparse matrices derived by the finite element method, a solution method that can be computed in parallel is required to take advantage of their sparsity. Iterative methods are one group of available methods, but they may not converge. In contrast, direct methods can solve such equations. We can use the multifrontal method as a part of a direct method to utilize two factors mentioned above. This paper explores how to implement the method that incorporates parallelization using MPI to achieve efficient solution in a variety of environments. Numerical experiments using sequential calculations were conducted as a preparatory step for parallelization. The results showed that there was still a large difference in execution time between the existing library and the application created here, especially in the factorization, which is the core of the multifrontal method. Therefore, it is necessary to parallelize the factorization operation to achieve efficient computation and to address bottlenecks that cannot be parallelized in the future.

In this study, to deal with complex moving boundary problems, we have extended s-version of finite element method (SFEM) to large-scale parallel analysis. The proposed method achieves both high accuracy and low computational cost by superimposing higher resolution arbitrary local meshes on structured coarser meshes based on interface capturing method which represents the entire domain. And we have improved the accuracy of integration by using B-spline functions as basis functions of the structured meshes. In addition, we apply a parallelization method based on overlapping domain decomposition to the proposed method and perform a strong scaling test to evaluate its performance.

The metal additive manufacturing problems can be modeled by the one way coupling problem from a heat conduction to a thermal elastic plastic analysis. It costs a lot of time and temperature steps to analyze the problems. To reduce the numbers of these steps, our previous studies used the balancing domain decomposition method as a parallel strategy, and a simplified heat source model. The model allows to sequentially heat an entire layer one by one, and this process continues until all layers are simulated. However, it was only applied to a simulation of depositing a plate. Thus, this study focuses on applying the model to a shape other than a plate with the balancing domain decomposition method. Especially, a half pipe model was considered. The paper presents how to find parameters of the simplified heat source model on the half pipe model. One of numerical results showed a speedup of more than one hundred times. They were also verified and validated.

A framework based on a partitioned stress integration technique was proposed by the present authors for a general combined elastic-plastic and creep constitutive model. It was developed to analyze a structure used in a high temperature environment. In the present study, a thruster nozzle model subjected to thermal strain is analyzed using the framework to verify it. The Ohno-Wang model and the Norton-Bailey model are used for the elastic-plastic model and the creep model, respectively. This combined model is also verified..

The main computations in finite element analysis are basic linear algebra operations on matrices and vectors, and even load distribution is suitable for these parallel computations. Therefore, parallel FEM codes implemented with OpenMP and simple scheduling often achieve good efficiency in conventional multi-core processors. However, in recent years, desktop CPUs such as Intel's Alder Lake and Apple's M1 have adopted heterogeneous architectures with high-efficiency and high-performance cores. Therefore, it is unclear whether the conventional parallel FEM code can extract the processor's performance on those parallel computers. This research evaluates the performance of a heterogeneous processor using a parallel FEM code that uses the conjugate gradient method as a linear solver and discusses the results.

When the interior shape is determined, the frequency range to be reduced, which is a particular problem, is determined. Until now, there has been no noise reduction countermeasure method using information on resonant frequency such as strain and kinetic energy density. For the first time in this report, it is shown that noise reduction of the resonant frequency, existing in the problematic frequency, can be effectively obtained after reducing the plate thickness from the energy density distribution. The greatest advantage of this method is that, unlike conventional optimization methods, it is possible to take countermeasures interactively and extremely reasonably, and systematization to draw out its effectiveness will also be discussed.

The purpose of this research is to develop a simple sound-reducing shade to enjoy playing music at home. The requirements for the shade are relatively inexpensive, foldable, suitable size and acoustic environment for playing, and most importantly sound dampening ability. Normally, the development of such a product requires many prototypes and verifications, but in this research, by utilizing finite element analysis (FEM), it is possible to find the optimum material and shape without producing a large number of prototypes. In this paper, we examined the performance of sound-reducing shades by investigating existing products, and in order to solve the problem with them, we designed a new sound-reducing shade that incorporates the ideas of Origami and Kirigami engineering. We also report the results of the feasibility study by FEM analysis of the sound-reducing shade.

The double structure, in which one hollow member is installed in parallel along the axial direction with another and two members are joined by foam material, on the inside and outside of the axial direction has been shown to be lightweight, and the initial peak load value can be reduced while maintaining the energy absorption amount. At that time, if the cross section is small and the plate thickness is thin, it can be made inexpensive even by hydroforming, so as an ideal combination, the inside should have a reversed spiral origami structure of ultra-thin steel plate, and the outside should have a normal steel plate reversed twisted origami structure by a partial heating rotation molding method that can be formed at an extremely low cost regardless of the plate thickness or the size of the cross-sectional area. Among many design parameters, such as the characteristics of the foam material that joins the internal and external parts, we will try to optimize the design of the extremely difficult nonlinear problem.